Pneumatic hammer

ABSTRACT

A pneumatic hammer is provided with an adjusting piston (37) dependent on the supply pressure, which adjusts the stroke length of the working piston (16). Thereby, the same pneumatic hammer may be operated both at low and high supply pressures. With high supply pressures, either the early ending of the acceleration phase or the early start of the compression phase or the shortening of the working cylinder shortens the stroke length. Thereby, the pneumatic hammer performs impacts with a substantially constant single-impact energy, regardless of the supply pressure. High supply pressures increase the impact frequency. This results in a considerably improved efficiency at a high drill capacity, a reduced wear and a reduced risk of ruptures of the components of the hammer.

BACKGROUND OF THE INVENTION

The invention relates to a pneumatic hammer of the kind mentioned in theprecharacterizing part of claim 1.

Such pneumatic hammers are used for ground or rock drilling. They may beimplemented in connection with drilling machines that advance and rotatedrill rods with a drill bit from a boring frame. In this case, thepneumatic hammer is generally designed as a in-hole hammer which isarranged immediately behind the drill bit in the drill rods. Further,pneumatic hammers may be designed as hand-held hammers, so-calledcompressed air hammers, which are operated by hand in order to dodemolition work or ground and rock work. With a hand-held hammer, thedrill bit generally is a simple trepan.

In pneumatic hammers with pin drill bits, the impact energy supplied bythe working piston is transmitted to the hard metal pins or bezels forcleaving rock via the drill bit. The impact frequency is determined bythe quantity of compressed air supplied or by the quantity transmittedby the pneumatic hammer. By rotating the entire drilling tool, thebottom of the bore hole is cleft and stripped and the drilling materialis transported to the outside by the relaxing and outflowing dischargeair in the annular gap between the drill rod and the inner wall of thedrill rod.

The drilling capacity is chiefly determined by the following factors:

the single impact energy imparted on the drill bit by the working pistonduring every blow;

the number and the surface of the drill bit pins on which the impactenergy is distributed and which transform that energy into penetrationand cleaving work;

the impact frequency;

the pressure of the drilling tool on the bottom of the bore hole;

the removal of the drillings or the purging or rinsing of the bottom ofthe bore hole to clean the same of the drillings.

The drive energy required for pneumatic hammers is supplied bycompressors. Normally, the supply pressure is about 7 to 10 bar and thesupply quantity is about 5 m³ /min.

Recently, high pressure compressors are used on building sites thatsupply a pressure in the magnitude of 20 bars. Such high pressurecompressors are also used to drive the pneumatic hammers used on abuilding site, even if these pneumatic hammers were originally designedfor pressures between 7 and 10 bars. For such high pressure operation,the principle of these pneumatic hammers has not been changed; onlycertain components of the hammer have been provided with a greaterstrength or a greater thickness. This results in the same pneumatichammers being operated in a wide range of supply pressures between 7 and25 bars. With a higher supply pressure, the impact frequency and theimpact energy will increase, but the drilling capacity is not enhancedcorrespondingly. This is due to the fact that the impact energy perdrill bit pin is essential for the drilling capacity. The drillingcapacity will only be optimal, if the impact energy per drill bit pin ismaintained in a certain range. Above this range, the cleaving depth ofthe rock (cleaving work) is not substantially improved, although theconsumption of compressed air increases vastly. Thus, the actualdrilling capacity is far behind the installed power of the compressor,which results in a low efficiency. Additionally, a high impact energy ofthe working piston generates a jarring blow on the anvil. Such jarringblows cause an enormous stress on the drill bit shaft and the workingpiston, often resulting in ruptures of shafts and pistons. In manuallyoperated pneumatic hammers, the jarring blows caused by an excessivesupply pressure entail serious physical stresses on the operator,including the risk of detrimental effects on his health and inparticular on the skeletal structure.

The operator of a drilling device will usually obtain the drillingtools, the compressor, the pneumatic hammer and the drill bit fromdifferent manufacturers, respectively. As a rule, this leads to anuntuned combination of elements being implemented. The operator is notable to select the components such that an optimal drilling capacitywith a high efficiency can be obtained with a simultaneous low stress onthe material.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a pneumatic hammer that maybe operated at different supply pressures and, in a wide range of supplypressures, yields a high drilling capacity with a high efficiency, whilesimultaneously keeping the stress on the material low.

The object is solved according to the invention with the features ofclaim 1.

In the pneumatic hammer of the present invention, an adjusting means isprovided at the front cylinder wall of the working cylinder, whichserves to change the stroke length of the working piston. Thus, theimpact energy imparted to the anvil by the working piston may be keptsubstantially constant in a wide range of supply pressures. At highsupply pressures of the compressed air, the piston stroke is reduced sothat the piston will hit on the anvil at substantially the same speed asit will at low supply pressures. Despite the great acceleration causedby a high supply pressure, the impact speed on the anvil is notsubstantially higher than at a low supply pressure, after all. Ofcourse, a high supply pressure and a correspondingly shortener stroke ofthe working piston will result in a higher impact frequency than wouldbe obtained at low supply pressures. This increases the drillingcapacity without reducing the efficiency. The volumetric consumption ofcompressed air is even reduced.

Preferably, the adjusting means changes the termination of theacceleration phase at the return stroke of the working piston. Thus, thelength of the return stroke is changed by changing the kinetic energyimparted to the working cylinder.

in general, it is possible to provide a pneumatic hammer with anadjusting means that is either mounted directly on the hammer housing ormay be remote-controlled by means of a transmission device. It is alsopossible to provide a pneumatic adjusting means, the pressure of whichmay be adjusted manually irrespective of the supply pressure of thecompressed air. Such manual adjusting means allow a user to influencethe stroke of the working piston.

In many instances, the operator is not able to adjust the correct strokelength. According to a preferred embodiment it is therefore provided toautomatically control the stroke length depending on the supplypressure. This automatic adjusting means is arranged within thepneumatic hammer so that all pressure losses in the conduit system orthe rods leading to the pneumatic hammer are taken into account. Thesupply pressure actuating the adjusting means is not the pressuresupplied by the compressor, but the pressure immediately present at thepneumatic hammer, which also causes the acceleration of the workingpiston.

The supply pressure at the pneumatic hammer does not have to be usedunchanged for controlling the djusting means. It is also possible toeffect a proportional pressure transformation, for instance, and tocontrol the adjusting means with a pressure depending on the supplypressure.

In addition to the automatic control of the adjusting means, a manualadjusting means may be provided, for instance, in order to adjust theimpact energy to the number drill bit pins.

Preferably, the invention is applicable with in-hole hammers that arearranged in a drill rod, as well as with hand-held hammers anddemolition hammers. With the latter, maintaining the single-impactenergy prevents the transfer of reflected energy into the wrists andarms of the user and the occurrence of damages to the user's health.

In compressors having no adjustable air pressure, or in compressorsconnected to a plurality of air consumers that require air pressure, thepneumatic hammer automatically adapts itself to the supply pressure,which results in a substantially constant impact energy regardless ofthe supply pressure and that a high supply pressure merely increases theimpact frequency. The components of the pneumatic hammer are subjectedto lesser stresses and their service life is prolonged.

The following is a detailed description of embodiments of the inventionin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures

FIG. 1 shows the front portion of a pneumatic hammer as an in-holehammer in a drill rod,

FIG. 2 shows the rear portion of the in-hole hammer of FIG. 1,

FIG. 3 is an upscaled illustration of the adjusting means arranged atthe front end of the working cylinder,

FIG. 4 shows an embodiment slightly modified with respect to that ofFIG. 3,

FIG. 5 shows an embodiment in which the adjusting means has a controlsleeve,

FIG. 6 shows an embodiment without a restoring spring in the adjustingmeans,

FIG. 7 shows an embodiment modified with respect to that of FIG. 6, and

FIG. 8 shows an embodiment modified with respect to that of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The pneumatic hammer illustrated in FIGS. 1 and 2 is a in-hole hammerwith an elongated tubular hammer casing 10, from the front end of whichthe head 12 of a drill bit 11 protrudes. The drill bit head 12 isprovided with hard metal pins (not illustrated). The shaft 13 of thedrill bit 11 extends into the hammer casing 10. Through a key toothing,the shaft engages an adapter 14 screwed into the hammer casing 10, inorder to transmit the rotation of the hammer casing to the drill bit 11.The drill bit shaft 13 is guided for limited longitudinal displacementso that, in case of impacts on the rear end of the shaft 13, the drillbit 11 can shoot forward with respect to the casing 10. The rear end ofthe drill bit shaft 13 forms the anvil 15 on which the working piston 16beats. The working piston 16 consists of a piston body 17 with sealinggrooves that beats against the anvil 15. A bore 19 extends through theentire length of the piston 16, which is aligned with a longitudinalbore 10 of the drill bit 11. The head 12 of the drill bit is providedwith outlets 21 that are connected with the longitudinal bore 20. Theexpanded discharge air of the pneumatic hammer escapes from theseoutlets for washing back the drilling material from the bottom of thebore hole.

The piston 16 is guided for longitudinal displacement within the tubularinner cylinder 22, the front cylinder chamber facing the drill bit 11being designated by the reference number 23, while the rear cylinderchamber facing away from the drill bit bears the reference numeral 24.The inner cylinder 22 is enclosed by an annular channel 25 through whichthe compressed air is transported over the entire length of the innercylinder 22. The inner cylinder 22 has radial control bores 26 and 27,the control bore 26 cooperating with a front control surface 28 and thecontrol bore 27 co-operating with a rear control surface 29 of thecylinder body 17. Moreover, the rear end portion of the inner cylinder22 is provided with a support bore 30 through which compressed airreaches the rear cylinder chamber 24.

Provided at the front end of the working cylinder, there is a guidesleeve 31 fixedly mounted in the hammer casing for a sealed guiding ofthe shaft 18 of the working piston.

The rear cylinder chamber 24 is limited to the rear by an insert 36 thatreceives the rear adjusting means 32. The adjusting means 32 includesthe adjusting piston 38 displaceable in a control cylinder 39 of theinsert 36 and from which a control tube 40 projects forward whichextends through a bore of the front cylinder wall 41. The interior ofthe control tube 40 is always in pneumatic communication with thelongitudinal bore 20 and the inside of the control cylinder 39 so thatthe low relaxed pressure always prevails in the control cylinder 39. Aspring 42 is provided in the control cylinder 42 that presses theadjusting piston backward. The rear end of the adjusting piston 38 isconnected to a pressure chamber 43 in which the supply pressureconstantly prevails.

According to FIG. 2, a check valve 44 is arranged behind the pressurechamber 43, which, in case that pressing water should rise from thedrill bit against the compressed air supplied, will block the path ofsuch water. The check valve 44 is actuatable only in the direction fromthe drill rod 45 to the bottom of the bore hole, but not in the reversedirection.

The rear end of the hammer casing 10 is connected to the front end ofthe drill rod 45 through an insert member 46, a key toothing 47 of theinsert member 46 engaging with a key toothing of a sleeve 48 screwedinto the hammer casing. The key toothings permit a limited axialdisplacement of the hammer casing with respect tot he drill rod 45. Aspring 49 is supported on a support ring 50 which in turn is supportedon the end of the key toothing of the sleeve 48. The spring 49 pressesthe fixed inner casing parts of the hammer axially together and permitsdisplacement of these parts due to vibrations.

From the drill rod 45, the compressed air supplied reaches the pressurechamber 43 and the annular channel 25 through the hollow insert 46 andvia the check valve 44.

According to FIG. 3, the adjusting means 37 arranged at the front end ofthe working cylinder for changing the end of the acceleration phase isintegrated into the drill bit shaft 13. It has an annular control piston55 that is axially displaceable within a control cylinder 56 provided inthe shaft 13 and from which a control tube 57 projects towards the bore19 of the working piston. The control tube 57 may enter the bore 19 ofthe control piston 56. If, during the return stroke, the front end 19aof the bore 19 passes the rear edge 57a of the control tube 57, thepressure in the front cylinder chamber 23 is relieved through the insideof the control tube 57 towards the pressure-free axial bore 20.

The adjusting cylinder 61 in which the adjusting piston 55 moves, isconnected to the pressurized annular channel 25 through a channel 58 sothat the supply pressure acts on the annular surface of the controlpiston 55. This supply pressure is counteracted by the spring 59. Whenthe force of the control piston generated by the supply pressure exceedsthe force of the spring 59, the control tube 57 is displaced forwardwithin the working cylinder. This means that the position of the rearedge 57a changes according to the supply pressure. At higher supplypressures, the compression phase is shortened since, starting from thefront end position of the working cylinder, the rear edge 57a is passedby earlier than at lower supply pressures. Thereby, a lesser energy isimparted to the piston during the return stroke at high supplypressures, which results in the forming of a pressure cushion with alower compression in the rear cylinder chamber 24. The return stroke(and, accordingly, the working stroke) of the working piston isshortened.

The pneumatic hammer depicted in FIGS. 1 to 3 operates as follows:

In FIG. 1, the piston 16 is illustrated as being in its front endposition in which the shaft 18 abuts the anvil 15. The front cylinderchamber 23 is reduced to a minimum and is connected to the pressure inthe annular channel 25 through the control bore 26. In this situation,the return stroke of the working piston 16 begins since the rearcylinder chamber 24 is connected to the pressureless longitudinal bore20 of the drill bit through the bore 19. During the return stroke, theworking piston 16 experiences an acceleration phase. The pressureprevailing in the front cylinder chamber 23 and acting on the frontcontrol surface 28 accelerates the working piston. This accelerationphase will last until the front edge 19a of the working piston 16 hasleft the rear end 57a of the control tube 57. The correspondingacceleration section BA is marked in FIG. 3. After this, the cylinderchamber 23 is connected to the pressureless axial bore 20. Theacceleration is followed by an idle phase in which the return stroke ofthe working piston is not driven. The air displaced from the rearcylinder chamber 24 is discharged through the bore 19 in the workingpiston.

When the rear control surface 29 of the working piston reaches the frontend of the control tube 40, the idle phase is ended. Next to follow isthe compression phase in which the air in the annular chamber of theworking cylinder surrounding the control tube 40 is compressed. Thecontrol tube 40 now closes the opening of the bore 19. The air trappedin the cylinder chamber 24 forms an air cushion that slows down therearward movement of the working piston. Now the working stroke iseffected in which the air cushion compressed in the cylinder chamber 24expands and drives the working piston in the direction of impact. Thisdriving force is even augmented by the air passing through the supportbore 30. The drive phase ends when the rear control edge 29 of theworking piston has passed the front end of the control tube 40. Thedrive section, in which the working piston is accelerated in thedirection of the impact, is indicated by AA in FIG. 1.

At the end of the working stroke, the shaft 18 of the working pistonhits the anvil 15, an air cushion having been formed in the frontcylinder chamber 23 short before the impact.

The operation described before refers to cases where the supply pressureof the compressed air has a comparatively low value of about 7 to 10bars. Such a pressure in the pressure chamber 43 is overcome by thespring 42 so that the adjusting piston 38 is moved into its rear endposition against this pressure and that the control tube 40 also takesits rear end position.

If the control pressure is higher, the adjusting tube 57 is advancedtogether with the control tube 40, the distance of advancement beingdependent on the supply pressure. With a higher supply pressure, theacceleration phase is terminated earlier, i.e. it is shortened.Moreover, the control surface 29 reaches the front end of the controltube 40 earlier so that the compression phase will begin earlier. Thisreduces the stroke of the piston (return stroke) so that the followingworking stroke of the working piston begins at a location closer to thefront side. At a higher supply pressure, the stroke of the workingpiston is reduced so that, despite the higher supply pressure, the speedat which the working piston hits on the anvil is substantially the sameas the impact speed that is obtained at a lesser supply pressure andwith the control tube 40 withdrawn.

The advanced position of the control tube 40 may be selected such that,during the return stroke, the acceleration phase and the compressionphase follow each other immediately or even overlap without anintermediate idle phase.

The embodiment of FIG. 4 differs from that of FIG. 3 only in that theadjusting means 37 is not integrated into the shaft of the drill bit 12,but is accommodated in a block 60 at which the anvil 15 is provided andwhich abuts the shaft 13 with its front end. The adjusting cylinder 61of the adjusting means 37 closed by the control piston 55 is connectedto the annular channel 25 and permanently connected to the supplypressure. A bore 62 extends from the cylinder 56 to the axial bore 20 ofthe drill bit.

According to FIG. 5, the adjusting means 37 is also arranged at thefront end of the working cylinder. The adjusting element consists of ahollow control jacket 65 having an annular collar formed thereon whichforms the control piston 66. A spring 59 presses the control piston 66and the control jacket 65 towards the working cylinder. The pressureexerted by the spring 59 is counteracted by the supply pressureprevailing in the annular space 61. The cylinder chamber containing thespring 59 is connected to the axial bore 20 of the drill bit throughbores 67 and bores 68 in the shaft, and, therefore, it is pressure-free.

In this embodiment, the working piston 16 has a shaft 18 that enters thecontrol jacket 65 and hits against the anvil 15. During the returnstroke, the acceleration phase is ended when the rear ends of thegrooves 35 in the shaft 18 reach the rear edge 65aof the control jacket65. With high supply pressures, this will occur earlier than with lowsupply pressures. In this way, the return stroke of the working pistonis reduced when a high supply pressure prevails.

The embodiment of FIG. 6 largely corresponds to the embodiment of FIGS.1 to 3 so that the following description is limited to the differences.The control tube 57 that extends towards the cylinder chamber 23 of theworking cylinder, has a tubular prolongation 57b pointing to theopposite direction (i.e. forward), which is sealingly movable in theaxial bore 20 of the drill bit shaft 13. The outer diameter of theprolongation 57b is smaller than that of the rearward directed mainportion of the control tube 57 so that the control piston 55 hasopposite piston surfaces of different size.

The adjusting piston 55 divides the adjusting cylinder into a firstcylinder chamber 61a and a second cylinder chamber 61b. The firstcylinder chamber 61a is in permanent connection with the front cylinderchamber 23a of the working cylinder through the bore 58. The secondcylinder chamber 61b is completely sealed by the adjusting piston 55 andthe prolongation 57b and is connected to the first cylinder chamber 61aonly through a throttle bore 70 extending through the adjusting piston55.

In the front end position of the working piston 16, as depicted in FIG.6, i.e. at the beginning of the return stroke, the rear end 57a of thecontrol tube 57 plunges into the channel 19 of the working cylinder sothat the front cylinder chamber 23 is cut off from the pressure-freeaxial bore 20. This cylinder chamber is thus supplied with compressedair via the bores 26 from the annular channel 25. This pressure reachesthe first cylinder chamber 61a of the adjusting piston through thechannel 58. Thereby, the adjusting piston 55 is deplaced to the left, asshown in FIG. 6, whereby the air in the second cylinder chamber 61b iscompressed. This compression is the greater the greater the supplypressure prevailing in the first cylinder chamber 61a is. The supplypressure increasing, the control tube 57 is drawn into the drill bitshaft so that its end 57a moves forward. When the piston is returnedafter the impact of the piston 16 on the anvil 15, the end 19a will movealong the end 57a of the control tube, whereby the pressure in the frontcylinder chamber 23 may expand into the axial bore 20. The firstcylinder chamber 61a will become pressure-free and the air contained inthe second cylinder chamber 61b expands and moves the adjusting piston55 back into the (right) end position which is the initial position ofthe adjusting piston and the control tube for the next stroke of theworking piston. The throttle bore 70 serves as a charging andcompensating bore for the cylinder chamber 61b. It is dimensioned suchthat the time required for a pressure compensation between the cylinderchambers 61a and 61b is much longer than the duration of a stroke of theworking piston. The control tube 57 will meet the working piston in itsrear end position, respectively, and, during the impact, takes aposition that corresponds to the supply pressure. This position ismaintained until the working piston has left the control tube again andthe cylinder chamber 23 becomes pressure-free.

The different sizes of the piston surfaces of the adjusting piston 55ensure that the adjusting piston will return to its (right) homeposition, if the same pressure prevails in both cylinder chambers 61aand 61b. This effect is even reinforced by the suction effect generatedwhen the working piston 16 leaves the front end 57a of the control tube.

The embodiment of FIG. 7 differs from that of FIG. 6 only in that afurther throttle bore 71 is provided in the wall of the prolongation 57bof the control tube 57. Only when the control tube 57 is extended almostcompletely, will this throttle bore 71 leading into the axial bore 20 belocated in the area of the second cylinder chamber 61b of the adjustingcylinder. The throttle bore 71 compensates the possibly building boostpressure of the second cylinder chamber 61b, thereby creating constantinitial conditions for the control tube 57 at every switching. Further,the bore 71 has the effect that condensation water that might gather inthe second cylinder chamber 61b, ground water, oil and other liquids arepurged into the axial bore 20.

The embodiment of FIG. 8 corresponds to that of FIG. 7, differing onlyin that the piston 55 has no throttle bore 70. Only the prolongation 57bof the control tube 57 is provided with a throttle bore 71 thatcorresponds to that of FIG. 7. The cylinder chamber 61b is discharged orneutralized in the respective switching position only through thethrottle bore 71. It is the advantage of this embodiment that thecontrol tube 57 travels longer displacement paths so that the stroke ofthe working piston changes a lot in dependence on the supply pressure.It is a further advantage that a back pressure building in the axialbore 20 influences the adjusting means 37 such that the stroke of theworking piston is prolongated and the impact capacity is increased.

Although a preferred embodiment of the invention has been specificallyillustrated and described herein, it is to be understood that minorvariations may be made in the apparatus without departing from thespirit and scope of the invention, as defined the appended claims.

I claim:
 1. A pneumatic hammer having a working piston (16) movable in aworking cylinder, said piston imparting impacts onto a drill bit via ananvil (15), and control members provided at said working cylinder andsaid working piston, which control a supply of compressed air to frontand rear cylinder chambers (23, 24) at both ends of said working pistonand which cooperate such that, during a return stroke, said workingpiston performs an acceleration phase and an air compression phase andthat, during a subsequent forward directed working stroke, said workingpiston performs a drive phase and an impact on said anvil(15),characterized in that at a front end of said working cylinder thereis provided a reciprocable adjusting means (37) for adjusting the lengthof the return stroke of said working piston in dependence on the supplypressure of the compressed air.
 2. The pneumatic hammer of claim 1,wherein said adjusting means (37) is controlled by the supply pressuresuch that, in case of a higher supply pressure, the stroke length isreduced.
 3. The pneumatic hammer of claim 1, wherein said adjustingmeans (37) adjusts one of said control members (57; 65) that determinesthe end of the acceleration phase (57; 65) phase in the return stroke.4. The pneumatic hammer of claim 1, wherein said adjusting means (37)adjusts one of said control members (40) that determines the beginningof the compression phase in dependence on the supply pressure.
 5. Thepneumatic hammer of claim 1, wherein said adjusting means (37) has anadjusting piston (55; 66) movable in an adjusting cylinder (61) andactuated by the supply pressure.
 6. The pneumatic hammer of claim 5,wherein said front cylinder chamber (23) of said working cylinder isconnected to a first cylinder chamber (61a) of said adjusting cylinder(61) and a second cylinder chamber (61b) of said adjusting cylindercommunicates with said first cylinder chamber (61a), and a dischargechannel (20) through first and second throttle bores, respectively (70;71).
 7. The pneumatic hammer of claim 6, wherein a piston surface ofsaid adjusting piston (55) defining a portion of said first cylinderchamber (61a) is smaller than a piston surface of said adjusting pistondefining a portion of said second cylinder chamber (61b).
 8. Thepneumatic hammer of claim 6, wherein said first throttle bore (70)extends through said adjusting piston (55).
 9. The pneumatic hammer ofclaim 6, wherein said second throttle bore (71) is provided through awall of said control tube (57).
 10. The pneumatic hammer of claim 9,wherein said second throttle bore (71) enters said second cylinderchamber (61b) only in a withdrawn position of said adjusting cylinder.11. The pneumatic hammer of claim 5, wherein said adjusting piston (55)is connected with a control tube (57) projecting into said workingcylinder, which is receivable may plunge into a longitudinal bore (19)of said working piston (16).
 12. The pneumatic hammer of claim 5,wherein said adjusting piston (66) is connected with a control sleeve(65) for receiving a shaft (18) of said working piston (16).
 13. Thepneumatic hammer of claim 12, wherein said adjusting piston (66) is anannular piston located on said control sleeve (65).